The present invention relates to a method and apparatus for sterilizing treatment-object water such as waste water discharged from fish farms, food and drink manufacturing facilities, or the like.
When removing microorganisms such as bacteria, molds or protozoa contained in waste water, the following method has been carried out, wherein a porous filter member that can collect such microorganisms is arranged in a water passage, so that the microorganisms are adhered or adsorbed to the filter member to be captured, thereby to purify the waste water.
There has been a further method, wherein electrodes are additionally inserted in the waste water for electrolysis to produce chlorine or ozone, thereby to exterminate the microorganisms contained in the waste water by the bactericidal action thereof.
However, such a filter member collects the microorganisms by receiving them in fine holes formed on the surface thereof, and thus, unless the microorganisms collide with the surface of the filter member or pass nearby, they can not be adsorbed thereto to be captured. Therefore, there has been an inevitable limit to the microorganism capturing effect.
Further, since the microorganisms are adsorbed to the filter member as noted above, the filter member eventually becomes saturated to release or discharge the microorganisms into the water passage. In view of this, it is considered to annihilate the adsorbed microorganisms by, for example, heating the filter member. However, there are those microorganisms that have resistance to heat. Thus, for securing the sterilizing effect, the filter member should be heated to a relatively high temperature.
Normally, microorganisms in a solution are charged at negative potential (reference literature: Masaki Matsuo, “Fundamentals and Application Technique of Electrolytic Water”, Gihodo Shuppan Co., Ltd.). This charging rate, however, is influenced by pH of the solution. Specifically, as alkalinity of the solution increases, the negative potential charging rate of the microorganisms increases, while, as acidity thereof increases, the positive potential charging rate increases (reference literature: “Conn Stumpf Biochemistry” 5th edition, Tokyo Kagaku Dozin Co., Ltd.). This state of things can be expressed by Chemical Formula 1 representing protein of the surface of a microorganism.
[Chemical Formula 1]
The reason is that, since H+ are few in an alkaline solution, H+ of protein are separated, so that as alkalinity of the solution increases, the negative potential charging rate of protein increases. On the other hand, since H+ are plentiful in an acidic solution, H+ are added to protein, so that as acidity increases, the positive potential charging rate of protein increases.
On the other hand, spore bacteria and yeasts (microorganisms) do not die out, but can survive even in, for example, strong alkaline or acidic water. FIG. 7 shows the survival rate of spore bacteria, wherein the axis of abscissas represents pH, and wherein L1 shows results after a lapse of one hour, while L2 shows results after a lapse of 24 hours. As clear from FIG. 7, it is seen that spore bacteria can survive even in a strong alkaline state of pH 12 or a strong acidic state of pH 2. FIG. 8 shows the number of bacteria of yeasts in a solution, wherein the axis of abscissas represents pH, and wherein L3 shows results after a lapse of one hour, while L4 shows results after a lapse of 24 hours. As clear from FIG. 8, it is seen that yeasts can also survive even in a strong alkaline state of pH 12 or a strong acidic state of pH 2. It is considered that the negative potential charging rate of microorganisms is quite high in the foregoing strong alkaline environment. Accordingly, if such a charging rate of microorganisms is controlled by adjusting pH, it is expected to efficiently collect microorganisms using electric charge of the microorganisms.
On the other hand, as the temperature of a solution increases, microorganisms in the solution become more active and more easily movable. Accordingly, by adjusting the temperature of the solution, it is also expected to enhance the collecting efficiency of the microorganisms.